Soybeans represent a significant world-wide food source, providing an excellent source of protein. As such, soybeans represent a potential alternative to meats.
Tofu and soymilk are two principal food products derived from soybean seeds. More than one billion people in China and Southeast Asia, it has been stated, rely on tofu as a major food protein source. (Proc. Int. Soya Protein Food Conf., American Soybean Assoc., p. 35, 1978). Soymilk is similarly an important source for food protein.
Soybean seeds also represent perhaps the most significant oilseed in the world and contain significant nutritive properties. Soybean oil has thus been considered to be the major vegetable oil produced and consumed in the United States, and more than 90% of this soybean oil is used in food products (World Soybean Research Conference III Proceeding, Shibles, R. (Ed.), 1985).
Soybeans contain two different saturated fatty acids, viz.--palmitic acid (16:0) and stearic acid (18:0). Palmitic acid is generally the major constituent, comprising some 70% of the total saturated fatty acid content.
The presence of the more typical level of palmitic acid may be considered undesirable for some applications. Extending back to the 1950's, the medical community has emphasized the role of fat intake in the pathogenesis of heart disease. The American Heart Association issued a series of reports dating from 1957 to the present; each report emphasized alteration of the diet by reducing intake of saturated fats. The Association has continued to recommend such a reduction and currently suggests that saturated fats comprise no more than 10% of the total calories of an individual's intake.
This is particularly true of saturated fatty acids having a chain length of 12 to 16, which includes palmitic acid. There is some evidence that stearic acid, having a chain length of 18, is less injurious or even perhaps beneficial with respect to artery disease.
A major competitor of soybeans for the vegetable oil market is canola. Canola has been promoted as a healthier oil than soybean oil because of its relatively lower saturated fatty acid content. It would be a significant advance to be able to provide soybean oil which would have a palmitic acid content similar to that of canola.
The formidable nature of the task to provide a saturated acid content in soybeans similar to that in canola can be appreciated from a recent report wherein it was stated that palmitic acid levels in soybean seed oil range from 9.3% to 17.4% within the world collection (Erickson et al., Journal of Heredity, 79, p. 465, 1988). The level of palmitic acid would have to be reduced substantially below the reported minimum of 9.3% to provide a palmitic acid content similar to that of canola. Thus, the palmitic acid content of canola would be expected to be below about 6%; and applicants are aware of reported palmitic acid levels down to about 4% or even slightly less.
The Erickson et al. article reports the inheritance of altered palmitic acid percentage in two soybean mutants, C1726 and C1727. The level of palmitic acid in C1726 averages 8.5%, and the range of values obtained is set forth. The lines resulting from crossing the mutant line C1726 with the commercial cultivar "Century" a re, also described.
It may also be desirable for some applications to develop a soybean line characterized by a low stearic acid content or a soybean line characterized by a low total saturated fatty acid content.
Despite the clear need for soybeans having a significantly reduced level of palmitic acid, this objective still remains to be achieved.